3. Why are there no machines with an efficiency of 1OO%?

A. Machines are not durable. B. Machines tend to deteriorate over time, C. Machines are not capable of handling heavy jobs, D. Machines are affected by external forces such as friction,

4. How is mass related to gravity? A. If you double the mass of an object, its gravitational force is tripled. B. If you double the mass of an object, its gravitational force is halved. C. If you double the mass of an object, its gravitational force is doubled.​